Dictionary of user-facing values - Amazon Neptune

Dictionary of user-facing values

Neptune does not store most user-facing values directly in the various indexes it maintains. Instead, it stores them separately in a dictionary and replaces them in the indexes with 8-byte identifiers.

  • All user-facing values that would go in S, P, or G indexes are stored in the dictionary in this way.

  • In the O index, numeric values are stored directly in the index (inlined). This includes date and datetime values (represented as milliseconds from the epoch).

  • All other user-facing values that would go in the O index are stored in the dictionary and represented in the index by IDs.

The dictionary contains a forward mapping of user-facing values to 8-byte IDs in a value_to_id index.

It stores the reverse mapping of 8-byte IDs to values in one of two indexes, depending on the size of the values:

  • An id_to_value index maps IDs to user-facing values that are smaller than 767 bytes after internal encoding.

  • An id_to_blob index maps IDs to user-facing values that are larger.